This invention relates to an improved toolmaker's square and in particular to an adjustable toolmaker's square that can be used equally as well as a checking tool or as a machining fixture.
The term toolmaker's square, as herein used, refers to an angle plate that is generally used in shop work by a pattern or toolmaker to check the squareness of a workpiece or the flatness of a surface. Typically the angle plate includes two fixed legs disposed at right angles to one another. The outer end faces of the two legs are accurately machined so that they form an exact 90.degree. angle. In use, one face is seated on the lapped surface of a surface plate or the like and a piece to be checked, as for squareness, is brought against the opposite or upraised face of the plate. When the plate is applied to the work, any deviation from a true right angular relation can be observed by the passage of light between the two abutting surfaces. This light test does not tell the machinist or inspector the amount of deviation involved and shims, feeler gauges or the like must generally be employed to determine the amount or degree of error that is involved. This method of testing and measuring is, of course, time consuming and inconvenient.
In previous attempts to overcome the disadvantages associated with a fixed angle plate, various kinds of direct reading devices have been developed that generally employ an upraised leg or blade that is pivotably connected to a more stable base leg. An indicator is usually connected between the two legs which provide a readable measurement of the relative position of the two legs. However, because of the mechanical connection between the two legs, these devices are generally subject to wear with usage and of being damaged in the event it is dropped or struck by a heavy object. Accordingly, the accuracy of the instrument becomes seriously impaired. Furthermore, the use of a large number of different moving parts and connections necessitates greater skill and care on the part of the user, increases the cost of manufacture and provides greater room for error.